The structure and mechanism of several multicenter oxidation systems are being investigated by spectroscopic and kinetic techniques. The main emphasis is on Complexes II and III from yeast, beef heart cytochrome oxidase and milk xanthine oxidase. The experimental approach emphasizes electron paramagnetic resonance, magnetic circular dichroism and Resonance Raman spectroscopy combined with potentiometric and stoichiometric oxidoreductive titrations and rapid reactions. Current effort is directed towards: (1) Potentiometric characterization of the cytochrome c-cytochrome oxidase complex, (2) Resonance Raman on heme a models and intermediates in the oxidase reaction, (3) purification and characterization of Complex II, (4) stopped-flow MCD kinetics of b and cl in complex III, (5) room temperature potentiometry of flavin radicals and MoV in xanthine oxidase, (6) attempted purification of the Fe/S protein from Complex III, (7) MCD characterization of cytochrome c peroxidase.